Luis M. Nieto

Stratigraphy and sedimentation in the Mediterranean Ridge diapiric belt

Abstract Two basic sediment types are recorded in the Mediterranean Ridge diapiric belt: the host sediment and the mud breccia. The host sediment consists of hemipelagic marl as dominant lithology, associated with sapropels and tephras as minor isochronous lithologies. A high resolution stratigraphy, which allows much more detailed and precise correlations than those based on biostratigraphy (essentially calcareous nannofossils) is applicable to the over 20 cores considered in this study, that were obtained during cruise TTR3-Leg 2 in 1993. The mud breccia is matrix-supported and contains submillimetric to pluricentimetric clasts in various amounts (Staffini et al., 1993). This lithology is consistently related to doming physiographic features of different size and shape (Camerlenghi et al., 1992), and to high reflectivity patches recorded on long-range side-scan sonar. The mud breccia can be intruded or extruded. The massive, course nature of the mud breccia recorded in the large majority of the 16 cores that contain this lithology may suggest intrusion. Cores from Napoli Dome, which is typically an active mud volcano (Cita et al., 1994), are fine-grained and very gaseous. Contacts between the mud breccia and the host sediment are mostly distinct, but may be gradational. Two cores document interlayering of the mud breccia with pelagic sediments, but not turbidites were ever recovered. Among the main results of the study we mention: the strong slope instability documented by the pelagic host sediments from the ridge diaperic belt (hiatuses, microfaults, hardgrounds); the wide distribution of diapiric features across the ridge axis (from the Inner Deformation Front to the Toronto Dome, some 50 km to the south); the age of the mud breccia (matrix essentially) which is consistently early-middle Miocene with some older elements, but strictly middle to Late Cretaneous for the southernmost Toronto Dome.

Jurassic Fe-Mn macro-oncoids from pelagic swells of the External Subbetic (Spain): evidences of microbial origin

Ferromanganesiferous macro-oncoids are distinctive from the External Subbetic Zone (Betic Cordillera, SE Spain) in relation to a major heterochronic unconformity, with a Middle Bathonian-Lower Oxfordian minimum hiatus and a Lowest Bathonian-Lowest Kimmeridgian maximum hiatus. The Fe-Mn macro-oncoids (43 mm mean-size) consist of microbial laminae with planar and arborescent to dendrolitic morphologies. Under petrographic microscopy, the planar morphologies are made up by condensed fibrillar meshworks whereas the dendrolitic ones are similar to Frutexites. Alternation between these two types of laminae reveals a rhythmic growth in the Fe-Mn macro-oncoids. Bacterial and fungal filaments are observed in SEM analyses as microbial mats constituted by a disperse web of filaments exhibiting a branching tube-like morphology with diameters ranging between 2 and 10 µm. Aggregates of coccoid-shaped forms are also registered by SEM analyses. Taxonomical approximation of the microbiota is complex, though in the thin section the condensed fibrillar meshworks look like cyanobacteria, and in SEM images the morphology of the filaments resembles fungal hyphae and green algae, whereas coccoids are assigned to cyanobacteria. The precipitation of Fe-Mn is related to the chemoorganotrophic behaviour of the benthic microbial communities, probably corresponding to the fungal mats and other chemosynthetic microbes. Inorganic precipitation mechanisms are regarded as insufficient for the accumulation of a significant amount of MnO. An efficient precipitation of Mn from natural water largely depended on the presence of Mn-oxidizing microorganisms. Sediment-starved zones of pelagic swells of the External Subbetic, located in the deep euphotic zone, were the best places for microbially mediated authigenesis.

Structural features of mud volcanoes and the fold system of the Mediterranean Ridge, south of Crete

Abstract New information on the geometry of the mud volcanoes, folds and faults located in the central part of the Mediterranean Ridge is provided from long range and deep-tow sidescan sonar images, high resolution seismic and low frequency echosounder profiles, and gravity cores obtained on the R/V Gelendzhik during the 1993 UNESCO-ESF Training Through Research cruise. Symmetrical gentle folds, with a mean wavelength of 750 m, deform predominantly Pliocene-Quaternary sediments, but also perhaps as old as Messinian. In most areas of the Mediterranean Ridge, the north-northeast directed subduction of the African plate below the Eurasian plate at the Hellenic arc produces folds with hinge lines subparallel to the trend of the ridge. However, the hinge lines of the folds curve around the southern part of the area with highest concentration of mud volcanoes and produce an irregular U-shape fold belt. Some of the folds show an intrusive nucleus and, in some of them, mud breccia appears to have flowed from the flanks of the folds into the troughs. The mud volcanoes consist of domes of interlayered pelagic sediments and mud breccias containing sediments and rock fragments of Late Aptian to Pleistocene ages. Mud breccia flows are mainly extruded radially from vents, although rare fissure extrusions are also observed. The mud volcanoes have an irregular to elliptical shape, with diameters up to 16 km. The distribution of mud volcanoes in the area is irregular, but they are more frequent in an area called the Olimpi Field. Faults in the uppermost part of the Mediterranean Ridge are rare. Most of the faults are normal and subparallel to fold limbs. In addition, N20°E and N100°E subvertical faults are found controlling the shape of the mud volcanoes.

Sedimentology of geomorphologically controlled Quaternary tufas in a valley in southern Spain

Four vertical facies sequences characterizing different environments have been identified in relation to two phases of tufa deposition (probably Pleistocene and Holocene) within a valley located in the central sector of the Betic Cordillera (southern Spain): (1) alluvial-fluvial (non-tufa) deposits, (2) fluvial tufa, (3) fluvio-lacustrine facies, and (4) spring with waterfall tufa. The first three created a stepped axial depositional system and the spring with waterfall tufa formed a transverse system. During the first phase of tufa construction, the vertical evolution in the axial system from alluvial-fluvial (non-tufa) to fluvio-lacustrine tufa deposits is interpreted as the consequence of geomorphological control. The evolution through time from a high-gradient and stepped fluvial system to a low-gradient fluvio-lacustrine system occurred upstream from where the progradation of the transverse, perched spring tufa system became narrower and finally dammed the valley. The tufa barrage caused an increase in the vertical accumulation within the axial system and a consequent upstream decrease of accommodation space and slope of the longitudinal profile. After a period of fluvial incision, tufa formed again during the Holocene in a high-gradient and stepped fluvial system.

Evolution of pelagic swells from hardground analysis (Bathonian–Oxfordian, Eastern External Subbetic, southern Spain)

The Middle Bathonian to Middle Oxfordian interval in the Eastern External Subbetic (Betic Cordillera, SE Spain) is characterized by Ammonitico Rosso facies including various stratigraphic breaks. Five hardground-bounded units are recognized in relation to hiatuses in the ammonite record at the following stratigraphic boundaries: Hg1 (Lower–Middle Bathonian), Hg2 (Middle–Upper Bathonian), Hg3 (Lower–Middle Callovian), Hg4 (Middle–Upper Callovian), and Hg5 (Callovian–Oxfordian). Interesting features of these hardgrounds include their microfacies, ferruginous crusts and macro-oncoids, taphonomy of macroinvertebrates, trace fossils, neptunian dykes, and the hiatuses associated with each of them. The main hardgrounds (Hg1, Hg2, and Hg5) contain trace fossils of the Cruziana and Trypanites ichnofacies as well as abundant fossil macroinvertebrates with taphonomic features evidencing corrasion, early diagenesis, and reworking, indicating substrate evolution from softground to hardground. Neptunian dykes affected the trace fossils and ammonoid moulds, and their walls and the hardground surfaces were colonized by ferruginous microbial crusts. These features are characteristic of the External Subbetic pelagic swells, where the absence of sedimentation, sediment bypassing and erosion, and early diagenesis during relative sea-level falls produced hardgrounds. The neptunian dykes are indicative of tectonic activity in the areas of pelagic swells. Ferruginous crusts and macro-oncoids developed only on hardground surfaces and neptunian dykes walls prior to deposition of condensed bioclastic beds, which are interpreted as the first deposits after hardground development and are related to the onset of transgression. The varying ranges of the gaps as well as lateral facies changes are related to different local paleobathymetry controlled by the activity of listric faults.

Composite Trace Fossil Assemblage in a Distal Carbonate Setting from the Tethys (Middle Jurassic, Betic Cordillera, Southern Spain)

Ichnological analysis of a Middle Jurassic carbonate surface from the Betic Cordillera (southern Spain) reveals a complex trace fossil assemblage, including softground Ophiomorpha, firmground Arenicolites, Thalassinoides and Gastrochaenolites, and hardground Trypanites as well as possible Gastrochaenolites. The ecological replacement in the macrobenthic community is interpreted according to successive suites that are controlled mainly by substrate consistency. Variations in composition and abundance of trace fossils between suites can be ecologically and/or taphonomically determined.

Median Subbetic Outcrops

The Iznalloz (IZ) section is located in the km 13 of the Granada-Moreda railway scarpment (N 37° 23′ 24.4″; E 03° 29′ 19.5″), 3 km east of the village of Iznalloz (Granada Province, Figs. 3.1 and 4.1). The study section pertains to the Toarcian of the Zegri Formation, and contains alternating marls and marly limestones in the lower part with nodular marly limestones (ammonitico rosso facies) in the upper part.

External Subbetic Outcrops

The Fuente Vidriera (FV) section is located on a valley slope (38° 03′ 19.8″ N; 02° 07′ 01.7″ W), 15 km west of the village of Barranda (Murcia Province), near Caravaca de la Cruz (Fig. 3.1). The study section pertains to the Upper Pliensbachian to uppermost Toarcian of the Zegri Formation, and contains alternating marls and marly limestones in the lower part with nodular marly limestones in the upper part.

The Betic External Zones

The Betic Cordillera is the major geological domain situated to the S and SE of the Iberian Peninsula. It is bounded by the Iberian Massif and the Iberian Mountain Range to the N and by the Atlantic Ocean and Mediterranean Sea to the SW, S, and SE. It belongs, along with other mountain ranges of North Africa, to the western segment of the Perimediterranean Alpine Orogen. In the Betic Cordillera, three main geological domains of greater rank are differentiated: the Betic External Zones, the Betic Internal Zones and the Campo de Gibraltar Complex.

An integrated analysis (microfacies and ichnology) of a shallow carbonate-platform succession: upper Aptian, Lower Cretaceous, Betic Cordillera

Four lithofacies and 12 microfacies types recognized in an upper Aptian section in the Sierra de Bedmar-Jódar (Prebetic of Jaén) represent shallow lagoonal environments (marl and marly limestone) and sand bars that delimited the lagoon. The lagoonal facies reflect subtidal restricted water circulation with low energy. The sand bar facies (intertidal environment) have upper surfaces that show the effects of supratidal and subaerial conditions. The presence of early fractures in particular lithofacies shows the importance of local synsedimentary tectonics during sedimentation. Thalassinoides, ?Arenicolites, Diplocraterion, Circolites, Gastrochaenolites and Trypanites are recorded in different beds of this section, reflecting various states of substrate consistency, in the form of firmground, hardground, and rockground. Whereas firmground conditions were dominant in the lower part of the section, hardgrounds and rockgrounds are mainly present in the upper part of the section. Four types of shallowing-upward elementary sequence are recognized. All the sequences show at the base mudstone or wackestone microfacies representing a lagoonal environment, overlain by sand-bar grain-pack-stone facies corresponding to a bar bounding the lagoon. The factors that controlled their development were carbonate production and tectonic movements.